Integrated cancellation circuit for RF converter spurious tones

Abstract

Techniques are disclosed for eliminating or otherwise sufficiently suppressing spurious signals. The techniques are particularly useful in applications such as those that employ aggressor frequency sources along with a frequency conversion or mixing function, and especially applications implemented as a system-on-chip. In the spur-training mode, a spur-canceller circuit identifies spurious tones associated with the host system to neutralize those tones when running in a normal mode. The tones are neutralized using a comb generator with variable phase and gain by way of cancellation with comb output signals having substantially the same amplitude and a phase that is 180° out of phase with the aggressor tone to be cancelled.

What is claimed is: 
     
       1. A method for canceling spurious tones in an RF converter having a mixer and an output, the method comprising:
 in a spur-training mode wherein a spurious tone associated with an aggressor source is present, generating a set of phase coherent harmonics of the aggressor source using a comb generator with variable phase and gain; 
 inserting the harmonics into a signal path prior to the mixer; 
 adjusting gain and phase of the comb generator while monitoring the output of the RF converter until the spurious tone is reduced to an acceptable level; and 
 after the spurious tone is reduced to an acceptable level, storing the corresponding gain and phase settings of the comb generator along with a corresponding aggressor source state identifier. 
 
     
     
       2. The method of  claim 1  further comprising:
 in a normal mode, retrieving comb generator gain and phase settings associated with the aggressor source state identifier to generate a comb output that includes a tone that will cancel the spurious tone; and 
 inserting the comb output into the signal path prior to the mixer, thereby canceling the spurious tone. 
 
     
     
       3. The method of  claim 1  wherein during the spur-training mode, the method further comprises the preliminary steps of:
 sweeping the aggressor source across all expected states, and monitoring the output of the RF converter; and 
 recording an identifier of each aggressor source state that results in a spurious tone to be cancelled in normal mode. 
 
     
     
       4. The method of  claim 1  wherein generating a set of phase coherent harmonics of the aggressor source using a comb generator with variable phase and gain comprises coupling energy from the aggressor source and filtering to minimize a peak comb output relative to the spurious tone. 
     
     
       5. The method of  claim 1  wherein storing the corresponding gain and phase settings of the comb generator along with a corresponding aggressor source state identifier comprises recording the corresponding gain and phase settings in a lookup table that is indexed by aggressor source state identifiers. 
     
     
       6. The method of  claim 5  wherein the method further comprises determining, in a normal mode, that the aggressor source is associated with the aggressor source state identifier, and that the aggressor source state identifier corresponds to an entry in the lookup table. 
     
     
       7. A system for canceling spurious tones in an RF converter having a mixer and an output, the system comprising:
 a comb generator with variable phase and gain for generating, in a spur-training mode wherein a spurious tone associated with an aggressor source is present, a set of phase coherent harmonics of the aggressor source; 
 a summer module for inserting the harmonics into a signal path prior to the mixer; 
 a digital controller for adjusting gain and phase of the comb generator while monitoring the output of the RF converter until the spurious tone is reduced to an acceptable level; and 
 a memory for storing, after the spurious tone is reduced to an acceptable level, the corresponding gain and phase settings of the comb generator along with a corresponding aggressor source state identifier. 
 
     
     
       8. The system of  claim 7  wherein the digital controller is further configured for retrieving from the memory, in a normal mode, comb generator gain and phase settings associated with the aggressor source state identifier to generate a comb output that includes a tone that will cancel the spurious tone, and the summer module is further configured for inserting the comb output into the signal path prior to the mixer, thereby canceling the spurious tone. 
     
     
       9. The system of  claim 7  wherein during the spur-training mode, the aggressor source is swept across all expected states, and the digital controller is further configured for monitoring the output of the RF converter and recording in the memory an identifier of each aggressor source state that results in a spurious tone to be cancelled in normal mode. 
     
     
       10. The system of  claim 7  wherein the comb generator with variable phase and gain for generating a set of phase coherent harmonics of the aggressor source is further configured for coupling energy from the aggressor source and filtering to minimize peak comb output relative to the spurious tone. 
     
     
       11. The system of  claim 7  wherein the memory for storing the corresponding gain and phase settings of the comb generator along with a corresponding aggressor source state identifier comprises a lookup table for recording the corresponding gain and phase settings and that is indexed by aggressor source state identifiers. 
     
     
       12. The system of  claim 11  wherein the digital controller is further configured for determining, in a normal mode, that the aggressor source is associated with the aggressor source state identifier, and that the aggressor source state identifier corresponds to an entry in the lookup table. 
     
     
       13. The system of  claim 7  wherein the system is included in a system-on-chip configuration. 
     
     
       14. The system of  claim 7  wherein the RF converter is a dual RF converter having first and second converter stages, and the aggressor source is a local oscillator associated with the first converter stage. 
     
     
       15. A system for canceling spurious tones in an RF converter having a mixer and an output, the system comprising:
 a comb generator with variable phase and gain for generating, in a spur-training mode wherein a spurious tone associated with an aggressor source is present, a set of phase coherent harmonics of the aggressor source; 
 a summer module for inserting the harmonics into a signal path prior to the mixer; 
 a digital controller for adjusting gain and phase of the comb generator while monitoring the output of the RF converter until the spurious tone is reduced to an acceptable level; and 
 a memory for storing, after the spurious tone is reduced to an acceptable level, the corresponding gain and phase settings of the comb generator along with a corresponding aggressor source state identifier; 
 wherein the system is included in a system-on-chip configuration, and the RF converter is a dual RF converter having first and second converter stages, and the aggressor source is a local oscillator associated with the first converter stage. 
 
     
     
       16. The system of  claim 15  wherein the digital controller is further configured for retrieving from the memory, in a normal mode, comb generator gain and phase settings associated with the aggressor source state identifier to generate a comb output that includes a tone that will cancel the spurious tone, and the summer module is further configured for inserting the comb output into the signal path prior to the mixer, thereby canceling the spurious tone. 
     
     
       17. The system of  claim 15  wherein during the spur-training mode, the aggressor source is swept across all expected states, and the digital controller is further configured for monitoring the output of the RF converter and recording in the memory an identifier of each aggressor source state that results in a spurious tone to be cancelled in normal mode. 
     
     
       18. The system of  claim 15  wherein the comb generator with variable phase and gain for generating a set of phase coherent harmonics of the aggressor source is further configured for coupling energy from the aggressor source. 
     
     
       19. The system of  claim 15  wherein the memory for storing the corresponding gain and phase settings of the comb generator along with a corresponding aggressor source state identifier comprises a lookup table for recording the corresponding gain and phase settings and that is indexed by aggressor source state identifiers. 
     
     
       20. The system of  claim 19  wherein the digital controller is further configured for determining, in a normal mode, that the aggressor source is associated with the aggressor source state identifier, and that the aggressor source state identifier corresponds to an entry in the lookup table.